A standard subsea installation comprises a mixture of hydraulically and electrically operated devices. The hydraulic devices are normally actuators for the operation of valves on the installation. The actuators may be controlled by electrically operated pilot valves that in its turn control control valves, all housed in a control module located at or near the well, the control valves directing the supply of fluid to each actuator, as dictated by the need for operation. Such a system is therefore called an electro-hydraulic system. In addition, injection valves for supplying chemicals may be needed and such valves are usually electric solenoid operated valves. Other devices are electrical of nature, such as sensors for monitoring various parameters in system, such as pressure and temperature, flow rates and sand and scale detectors. These usually communicate with the control system module via a dedicated cable, each sensor being connected separately to the control module, for receiving and transmitting signals and, in some cases, electric power.
The standard control module used in today's systems is housed in a container filled with an inert gas such as Nitrogen and pressurised at 1 bar to protect the electronics of the system. It contains the electronics for receiving signals from the sensor devices and for transmitting signals to a control station at a production vessel, such as a floating production storage and offloading vessel (FPSO), or other remote location. All the electrical pilot valves are also housed in the control module. The supply lines for hydraulic and chemical fluids are connected to the control module with lines extending therefrom to the hydraulic actuators and the chemical injection points as needed. This system is very inflexible. For example, it must be decided beforehand how many control valves will be needed. If more control valves will be needed then the control module must be pulled up and exchanged with a new and larger control module. Such an action requires the well to be shut down, resulting in lost production. Usually the control module is made larger than needed in case the system needs to be extended.
It has been proposed to use directly electrically operated valves, using electric motors, as this will be simpler and eliminate the need for large and costly hydraulic actuators and the use of pilot valves, since the actuators can be directly controlled.
An all-electric system will eliminate the need for hydraulic piping that is used in today's subsea installation, resulting in considerable savings, since not only must the pipes be carefully mounted, but they also need to be extensively tested for leaks and flushed clean. Another advantage with an all-electric system is the possibility of a large degree of modularisation. Electrically powered actuators can be made small and compact and are connected to the control module with a cheap and simple cable.
In an all-electric system it will be possible to configure it as a local area network (LAN), as is well known in many technical areas. Each device may have its own controller unit with a unique address and the electronics in the control-module having a micro processor, a bus controller, a memory unit and an input signal controller. Examples of such systems are described in WO 9914643 and WO 02054163, and in U.S. Pat. No. 5,941,966. It will enable devices to be removed and/or added to the system without shutting the whole system down. Any new device may easily be registered in the central control module by remotely reprogramming the control module processor.